Safe Loading Dose Without Current Weight
Use the last known weight of 179 lbs (81 kg) to calculate the loading dose, as this represents the most recent objective measurement available and is the standard of care when current weight cannot be obtained. 1
General Principles for Loading Dose Calculation
When a patient refuses to be weighed, the most appropriate approach depends on the specific medication being administered:
Weight-Based Dosing Strategy
For most medications requiring loading doses, use the most recent documented weight (in this case, 179 lbs or 81 kg) as the basis for calculation, as this provides the most accurate available data for dosing. 1
The timing of the last weight measurement matters less than having an objective measurement, particularly when the alternative is estimation or guessing, which introduces greater error and safety risk. 1
Medication-Specific Considerations
For anticoagulants (if applicable):
Unfractionated heparin (UFH): Use weight-based dosing of 60 U/kg loading dose with a suggested maximum of 4000 U, followed by 12 U/kg/h infusion with a maximum of 900 U/h. For a patient weighing 81 kg, this would be approximately 4000 U loading dose (at the cap). 2
Low molecular weight heparin (LMWH): Calculate based on actual body weight - enoxaparin 1 mg/kg subcutaneously. For 81 kg, this would be 81 mg. 2
GP IIb/IIIa inhibitors:
For antiplatelet agents (if applicable):
Aspirin: Loading dose of 162-325 mg (non-weight-based), which should be chewed for faster onset. 2
Clopidogrel: Loading dose of 300-600 mg (non-weight-based). 2
Prasugrel: Loading dose of 60 mg (non-weight-based), though contraindicated if weight <60 kg. At 81 kg, this patient is well above the weight threshold. 2
Ticagrelor: Loading dose of 180 mg (non-weight-based). 2
Critical Safety Considerations
For drugs with narrow therapeutic indices or high bleeding risk, using the last documented weight is safer than estimation, as it provides an objective reference point for dose calculation. 1
Document clearly in the medical record that the dose was calculated using the last known weight from [DATE] due to patient refusal to be weighed, and note the specific weight used (179 lbs/81 kg). 1
Monitor closely for adverse effects, particularly if there is reason to believe significant weight change has occurred since the last measurement. 2
For obese patients (BMI >30), some medications may require adjusted body weight rather than actual body weight for loading doses, though at 179 lbs this is unlikely to be a concern unless the patient is very short. 3, 4
When Last Weight May Be Inadequate
If the last weight is >6-12 months old or if there are obvious clinical signs of significant weight change (edema, cachexia, pregnancy), consider using clinical judgment to adjust the dose conservatively or use ideal body weight calculations as a safer alternative. 3
For drugs distributed primarily in lean tissue (aminoglycosides, neuromuscular blockers), ideal body weight may be more appropriate than actual body weight even when actual weight is known. 3